Thanks for your report.
I have sent you an email with a debug version of WinSCP to the address you have used to register on this forum.

Clicked the "Bypass authentication entirely" check box in the advanced settings and got the following message. Using version 5.13.2(Build 8455)

WinSCP 5.13.2

Error message:
Invalid access to memory.

Stack trace:
(008BC642) C5104_0
(008BE6AA) ____ExceptionHandler
(008BB464) __ExceptionHandler
(0006248E) ntdll.dll
(0000F15E) ntdll.dll.KiUserExceptionDispatcher
(006426AE) C2484_0
(00642861) C2484_0
(00642B7C) _ssh_connshare_log
(00671CE9) _select_result
(00737F8E) TSecureShell::HandleNetworkEvents
(00738252) TSecureShell::ProcessNetworkEvents
(0073783B) TSecureShell::WaitForData
(007329CD) TSecureShell::Init
(007322A2) TSecureShell::Open
(007B4C8B) TTerminal::Open
(006F1793) TTerminalThread::TerminalOpenEvent
(006EC7A8) TSignalThread::Execute
(000A317B) Userinterface::C20_0
(0001243B) kernel32.dll.BaseThreadInitThunk
(00038830) ntdll.dll
(00038800) ntdll.dll

(008BCCAD) C5104_0
(008BE287) _ReThrowException
(00732ADB) TSecureShell::Init
(007322A2) TSecureShell::Open
(007B4C8B) TTerminal::Open
(006F1793) TTerminalThread::TerminalOpenEvent
(006EC7A8) TSignalThread::Execute
(000A317B) Userinterface::C20_0
(0001243B) kernel32.dll.BaseThreadInitThunk
(00038830) ntdll.dll
(00038800) ntdll.dll
Authentication failed.

I know how to reproduce the problem or the problem happens frequently enough. I wish to be contacted by the WinSCP team to help resolving the problem.